I am trying to implement OAuth 2.0 Username-Password Flow and below is my code and debug log - any help is appreciated. [https://help.salesforce.com/help/doc/en/remoteaccess_oauth_username_password_flow.htm]

Http httpProtocol = new Http();   
HttpRequest request = new HttpRequest();
request.setHeader('Content-Type', 'application/json;');
request.setEndPoint('https://test.salesforce.com/services/oauth2/token');
request.setMethod('POST');
String strbody = '{"grant_type":"Password", "password":"MY PASSWORD + TOKEN", "username":"SANDBOX USER NAME",  "client_secret":"secret",   "client_id":"Client id from remote setttings"}';
request.setBody(strbody);
HttpResponse response = httpProtocol.send(request);
String jsonInput = response.getBody();
system.debug('jsonInput===>'+jsonInput);

Debug log - 

15:55:38.068 (68324000)|SYSTEM_METHOD_ENTRY|[5]|System.HttpRequest.setMethod(String)
15:55:38.068 (68346000)|SYSTEM_METHOD_EXIT|[5]|System.HttpRequest.setMethod(String)
15:55:38.068 (68350000)|STATEMENT_EXECUTE|[6]
15:55:38.068 (68356000)|HEAP_ALLOCATE|[6]|Bytes:357
15:55:38.068 (68381000)|VARIABLE_ASSIGNMENT|[6]|strbody|"{\"grant_type\":\"Passw (337 more) ..."
15:55:38.068 (68387000)|STATEMENT_EXECUTE|[7]
15:55:38.068 (68407000)|SYSTEM_METHOD_ENTRY|[7]|System.HttpRequest.setBody(String)
15:55:38.068 (68440000)|SYSTEM_METHOD_EXIT|[7]|System.HttpRequest.setBody(String)
15:55:38.068 (68445000)|STATEMENT_EXECUTE|[8]
15:55:38.068 (68478000)|SYSTEM_METHOD_ENTRY|[8]|System.Http.send(APEX_OBJECT)
15:55:38.068 (68568000)|CALLOUT_REQUEST|[8]|System.HttpRequest[Endpoint=https://test.salesforce.com/services/oauth2/token, Method=POST]
15:55:38.483 (483258000)|HEAP_ALLOCATE|[EXTERNAL]|Bytes:219
15:55:38.483 (483399000)|CALLOUT_RESPONSE|[8]|System.HttpResponse[Status=Bad Request, StatusCode=400]
15:55:38.483 (483424000)|HEAP_ALLOCATE|[8]|Bytes:96
15:55:38.483 (483444000)|SYSTEM_METHOD_EXIT|[8]|System.Http.send(APEX_OBJECT)
15:55:38.483 (483615000)|VARIABLE_ASSIGNMENT|[8]|response|"System.HttpResponse[Status=Bad Request, StatusCode=400]"|0x1b22c3f1
15:55:38.483 (483627000)|STATEMENT_EXECUTE|[9]
15:55:38.483 (483666000)|SYSTEM_METHOD_ENTRY|[9]|System.HttpResponse.getBody()
15:55:38.483 (483742000)|HEAP_ALLOCATE|[9]|Bytes:81
15:55:38.483 (483751000)|SYSTEM_METHOD_EXIT|[9]|System.HttpResponse.getBody()
15:55:38.483 (483780000)|VARIABLE_ASSIGNMENT|[9]|jsonInput|"{\"error\":\"unsupporte (61 more) ..."
15:55:38.483 (483786000)|STATEMENT_EXECUTE|[10]
15:55:38.483 (483794000)|HEAP_ALLOCATE|[10]|Bytes:13
15:55:38.483 (483980000)|HEAP_ALLOCATE|[10]|Bytes:94
15:55:38.483 (483999000)|SYSTEM_METHOD_ENTRY|[10]|System.debug(ANY)
15:55:38.484 (484025000)|USER_DEBUG|[10]|DEBUG|jsonInput===>{"error":"unsupported_grant_type","error_description":"grant type not supported"}